I know there is probably no hope left, even if one just considered that 3 unrelated persons remarked that the car smelled like a dead body (including the suspect's mother) and testing shows there was a dead body in there, this child is the only missing "body" in this motley group and the suspect has been proved to be lying her *advertiser censored* off. So....I understand the implications. I've tried to figure out some way for this all to make sense, with Caylee still alive. The only scenario I could come up with is:
1. Casey, possibly with help, killed someone (or someone else did and Casey is helping to cover it up).
2. Caylee saw either the killing, or the aftermath (disposing of the body, which spent some time in the trunk of the car in question).
3. The murderers are scared that Caylee will spill the beans on what she saw so they've squired her away somewhere.
The only (okay, not only) problem with this scenario is that one would think that instead of hiding Caylee, Casey would have tried to "talk" Caylee "out of" what she witnessed (i.e., to convince the child that she didn't really see anything or otherwise prevent the child from talking about it if questioned.) Also, at this late stage in the game with everyone thinking Caylee is dead, Casey would have produced the child and then claimed something like "I killed someone in self-defense and didn't want the child to tell on Casey. I don't know where the body is. Someone named Zenaida took the body."
I don't see any other scenarios where this child could be alive.